The present invention relates to systems and methods for measuring intrathoracic impedance (intracardiac, intravascular, subcutaneous, etc.) in an implantable medical device (IMD) system.
In systems employing IMDs such as pacemakers, defibrillators, and others, it has proven beneficial to provide the ability to measure intrathoracic impedance. Intrathoracic impedance measuring is performed by monitoring the voltage differential between pairs of spaced electrodes as current pulses are injected into those same leads or into other electrodes. Changes in the measured intrathoracic impedance may indicate certain disease conditions that can be addressed by delivery of therapy or alarm notification, for example. The efficacy of impedance monitoring to evaluate and monitor pulmonary edema and worsening congestive heart failure has been demonstrated in the OptiVol® Fluid Status Monitoring system provided by Medtronic, Inc. of Minneapolis, Minn.
Further improvements in the ability of an intrathoracic impedance measuring system to identify and monitor disease conditions would be useful.